In controlling the transmission of fluids in industrial processes, etc., it is often necessary to transmit the process fluid at a relatively high pressure through portions of the distribution system or process demanding high volume or flow rate of process fluid. As the high pressure process fluid travels through the distribution system or process, the pressure of the process fluid may be reduced at one or more points to supply a lower volume of the process fluid at a lower pressure to a sub-system that uses or consumes the process fluid.
Pressure reducing fluid regulators are typically used to reduce and control the pressure of a process fluid. In general, a pressure reducing fluid regulator varies the restriction through a valve that is serially interposed in the fluid flow path. In this manner, the pressure reducing fluid regulator can control the fluid flow rate and/or pressure provided at a downstream outlet of the regulator.
Some fluid regulators are set to allow a fluid to flow through the fluid regulator until an output pressure reaches a predetermined set pressure (e.g., a maximum downstream pressure), at which time a regulator stem retracts or extends and moves a plug toward an opening to restrict fluid flow through the regulator. If the output pressure decreases below the predetermined set pressure, the regulator stem moves in an opposite direction and moves the plug away from the opening allowing increased fluid flow through the regulator.
Typically, a fluid regulator includes a biasing element (e.g., a spring), a measuring element (e.g., a diaphragm), and a restricting element (e.g., a valve plug). Different size regulators are used for different applications and include a diaphragm and a spring of varying sizes to suit the particular application. The spring has a spring rate that is typically associated with the force change per unit change of length of the spring. The diaphragm has an effective area that corresponds to the area of the diaphragm that is effective in producing a force on, for example, a regulator stem. The effective area of the diaphragm may change depending on the position of the diaphragm within the fluid regulator. Typically, a diaphragm having a larger diameter will have a larger effective area compared to the effective area of a diaphragm having a smaller diameter.
Depending on the fluid regulator operational requirements, the spring rate, and the effective diaphragm area are selected based, at least in part, on Equation 1 below.PA=kX  Equation 1
Referring to Equation 1, P is the sensed pressure acting against the diaphragm, A is the effective diaphragm area (i.e., A), k is the spring rate (i.e., k), and X is the total compression of the spring. As illustrated by Equation 1, if the sensed pressure (i.e., P) and the total spring compression (i.e., X) are held constant, the effective diaphragm area is related to the spring rate such that as the effective diaphragm area is increased, the spring rate must also be increased. Likewise, as the effective diaphragm area is decreased, the spring rate must be decreased. In some applications (e.g., where limited mounting space is available), it may be desirable to decrease the diameter of the diaphragm to, for example, reduce the overall size of the regulator (e.g., width). Based on Equation 1, reducing the diaphragm area also requires decreasing the spring rate. However, decreasing the spring rate decreases the resulting force acting on, for example, the stem. In practice, using a spring that has a relatively low spring rate may cause regulator chatter (e.g., plug chatter) and decrease the overall performance of the fluid regulator.